Q. Why don't we have a day of fasting and tefillah for Ukraine like the Jews had in the Purim story?
A. The obvious answer is that we are lacking the united and recognized leadership provided by Mordechai and his Beis Din in those days.
Horav Shlomo Miller’s added that we indeed had a Taanis for that purpose, as Moetzes Gedolei Hatorah declared to include during Taanis Esther this year, Tefilos and Tehilim for those Kehilos and individuals.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a